1. Field of the Invention
The present invention relates to a packaging structure of a semiconductor device having a BGA (Ball Grid Array) type package structure (hereinafter, referred to as a BGA type semiconductor device) mounted on a circuit substrate such as a ceramic wiring board or the like and a packaging method of packaging the BGA type semiconductor device on the circuit substrate. More specifically, it relates to a packaging structure of a BGA type semiconductor device and its packaging method capable of assuring high stability against temperature of the circuit substrate after the semiconductor device is packaged.
2. Description of the Related Art
FIG. 3 is a cross-sectional view of a circuit substrate for use in describing the conventional packaging method of a BGA type semiconductor device. With reference to FIG. 3, a BGA type semiconductor device 102 is mounted on a ceramic wiring board 101 as a circuit substrate, and BGA balls 103 that are external terminals of the semiconductor device 102 are electrically connected to an electrode pad (not illustrated) on the ceramic wiring board by use of fixing means such as solder or the like.
However, when packaging a BGA type semiconductor device on a ceramic wiring board by use of fixing means such as solder, a great difference in the coefficient of thermal expansion between the semiconductor device and the ceramic wiring board may cause a distortion on the connection portion of the semiconductor device and the ceramic wiring board, depending on the temperature (heat cycle) after packaging the semiconductor device on the ceramic wiring board, hence producing a local stress on some part of the connected portion of the BGA balls, with some fear of destruction of the balls. Therefore, the above-mentioned packaging method cannot give a high stability to the connection of a semiconductor device and a ceramic wiring board.
For example, when a thermal shock cycle test at the cycle of -40.degree. C. (30 min), room temperature (5 min), 125.degree. C. (30 min) was performed there after packaging a BGA type semiconductor on a ceramic wiring board, a break occurred within 20 cycles due to a difference in the coefficient of thermal expansion of the semiconductor device and the ceramic wiring board.